RFR(S) JDK-8044738: Check attribute_length of EnclosingMethod attribute

[harold seigel]

Hi,

Please review this small fix for bug 8044738.  The fix adds a check that 
the attribute_length for the EnclosingMethod attribute is valid, and 
throws a ClassFormatError exception if it is not.

Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8044738/
Bug: https://bugs.openjdk.java.net/browse/JDK-8044738

The fix was tested with JCK Lang, VM and Api/java_lang tests, hotspot 
Jtreg tests, and Ute quick tests.

Thanks, Harold